*3.1.3. Adequate procedure of vaccine formulation*

The viruses used for vaccine production are harvested in live cells like chicken embryo. The bacteria used for vaccine production are culture in growth media like nutrient agar, etc. Similarly, the procedures for live attenuated, killed inactive vaccines, subunit vaccines differ from antigen to antigen. The adequate procedure for vaccine formulation will result in a maximum immune response from the antigen and hence a successful immune response.

#### *3.1.4. Proper storage and cold chain temperature*

Vaccines are to be manufactured in a plant and then after stored and transported to remote areas. Temperature has direct effect on the efficacy of vaccine [24]. The vaccines lose their potency with the passage of time; hence, they require proper cold temperatures to remain stable and viable for long periods of time. The proper storage and cold chain temperature of vaccine is of utmost importance; the vaccines must be stored below 4°C. The storage of food items, chemotherapeutic agents, specimens for pathological examinations, tissue samples for laboratory findings along with vaccine should be avoided [25]. During transportation, the maintenance of cold chain is a challenge for developing countries. A number of factors create hurdles in maintaining cold chain systems including loss of electric power, substandard refrigeration system, overchilling, etc. Moreover, the extra chilling of oil-based vaccines results in crystal formation of adjuvant material of vaccine like aluminum salts, etc. resulting in reduced potency of vaccines. The thermostable vaccines can be stored at 2–8°C and has more significance where cold chain temperature is not maintained and is less expensive [24]. Thermostable vaccines have some resistance to cold and hot environments, while freeze-dried vaccines should be preserved and stored at low temperatures in the refrigerator at 4°C and even during the transport of vaccine the cooling/ice blocks should be used to maintain low temperatures during transportation of vaccine. Freezing and thawing must be avoided. The vaccines must only be brought out of the refrigerator/freezer at the time of use at the farm. The live vaccines in poultry flocks must be used within 2 h of its reconstitution. Once they have been reconstituted, they drop their potency rapidly. The reconstituted vaccines should be used as early as possible and unused vaccines may be stored in the refrigerator for a maximum of 6 h; after that period the vaccines should be discarded.

The use of thermostable vaccines can be an alternative to overcome the difficulties related to cold chain and storage temperature [26]. The thermostable vaccines can maintain their potency and vaccinal activity for 1 year at 2–8°C and for 3 months up to 28°C in dried form [27]. Routes including intraocular, intranasal, paternal (injection) and oral (drinking water and feed) can be used for administration of thermostable vaccines [28, 29].

after its reconstitution in diluents, etc. Once the vaccine is reconstituted, the time limit is set. Vaccines must be used within 2 h of their reconstitution during winter and within 1 h of their reconstitution during summer. IB vaccines lose potency after 1 h of their reconstitution, while

Preventing Vaccine Failure in Poultry Flocks http://dx.doi.org/10.5772/intechopen.79330 87

There are many substances that have been used in poultry for immune stimulation. Some of them are vitamin E, selenium and levamisole [33, 34]. The selenium supplementation has effect on enhancing humoral immune response in chicks [35, 36]. The selenium supplementation increased natural resistance of increasing response of organisms to antigenic stimuli [37, 38]. The increased humoral antibody titers are observed when selenium is used in feed [39].

Some of the vaccines require a booster dose for successful immunization [2]. The booster dose is required after 10–20 days of the initial dose. The initial dose is required for priming of vaccine, while the booster is required for maximum protection against antigen. The lack of booster dose results in low antibody titers. As a result, vaccine failure may result. It has been documented that the priming with live attenuated vaccine followed by booster of killed vaccine and second booster with live vaccine provides best protection against Newcastle disease

An effective vaccine response may be obtained if the bird is healthy. The following recommendations/guidelines can overcome the shortcomings regarding prevention of vaccine failure.

All types of stresses mentioned earlier should be avoided before administration of vaccines to poultry birds. The temperature of the environment and sheds should be normal before vaccination. Moreover, the birds should be in a good physical condition before administration of vaccines. Stress suppresses the chicken's immune response, and during these conditions of stress, birds should not be vaccinated [41]. The stress on birds can be minimized by the use of

The adult birds may be dewormed before vaccination at least 15 days before injection of vaccine; moreover, diseased birds should be treated properly and be given vaccines after recov-

Some of the diseases in poultry have subclinical infections, like coccidiosis. The birds apparently seem health, but subclinical infections persist in birds over long periods of time, which

vitamins and minerals in drinking water before, during and after vaccination [13].

pox vaccines lose 50% of their potency after 1 h of their reconstitution [32].

[40]. However, subsequent inoculums are also required at regular intervals.

*3.1.10. Use of immune boosters*

*3.1.11. Booster dose*

**3.2. Host factors**

*3.2.1. Stress-free birds*

*3.2.2. Deworming before vaccination*

ery. Only healthy flocks should be vaccinated.

*3.2.3. Monitoring of subclinical infections*
